Arteriovenous Malformations

The technical challenges of surgically excising arteriovenous malformations (AVMs) located in the critical or deep portions of the brain make it crucial that the surgeon performing the operation is highly skilled and well versed in the appropriate approach to the AVM. Resection of AVMs, particularly those located in functional areas, requires precision and minimal disturbance to the surrounding brain tissue.

To enhance that precision, endoscope-assisted microsurgery has been employed at the Skull Base Institute. Endoscope-assisted microsurgery enhances magnification, illumination, and technical precision while the surgeon is dissecting the AVM core vessels and operating on AVMs that have deep extensions into the brain. With the advent of minimally invasive endoscopic techniques, the surgical resection of AVMs has become safer, thus significantly reducing complications.

Overview
Arteriovenous malformations involve an abnormal connection between one of the brain's arteries and veins. Approximately 0.14% of the US population is affected with AVMs. The incidence of AVM's is equal in both men and women.

AVMs are troublesome for many reasons. First, AVMs allow blood from the heart to bypass the brain's capillaries, which normally deliver oxygen and nutrients to the brain tissues. This may result in neurological deficits.

Meanwhile, the detoured blood causes increased pressure on the fragile wall of the AVM. The AVM may become swollen due to the effects of this pressure. The ballooned AVM can press down on the adjacent brain tissue, inducing seizures or causing compressive damage to surrounding brain tissue.

A much more serious complication is the risk of hemorrhage (bleeding). This can be a life threatening emergency, damaging surrounding brain tissue, and rarely in severe cases may even result in death. It has frequently been observed that small AVMs tend to bleed more frequently than larger ones. Once an AVM has bled, the re-bleed rate is 4% per year. Fortunately, hemorrhage from an AVM is rarely fatal (<10%), which is in contrast to the high mortality rate of ruptured aneurysms (>90%). However, neurological deficits can still result from the compression and destruction of the surrounding brain tissue.

Causes
Although most AVMs are congenital, the exact etiology of their formation is unknown. Researchers support that the abnormalities that occur in blood vessels in AVMs during embryonic or fetal development may be linked to genetic mutations in some cases. Some evidence also suggests that at least some of these lesions are acquired later in life as a result of injury to the central nervous system.

Symptoms
The presentation of AVMs varies from person to person. Unless the AVM enlarges or bleeds, they frequently cause no symptoms whatsoever.

AVMs as mentioned previously, may also present with new onset seizures. Seizures resulting from AVMs often occur after the age of twenty.

The symptoms of AVM hemorrhage include: sudden and severe headache, vomiting, vision change, abnormal weakness, decreased sensation, or a change in mental status. The headache, which often heralds hemorrhage from and AVM, is similar to a classic migraine.

Diagnosis
The work-up includes a complete neurological examination to detect any deficits. Additionally, 3-dimensional, spiral CT angiography or magnetic resonnance angiography (MRA) of the brain are used to diagnose AVMs. Video X-rays of blood vessels using injected dye (Angiography) can provide even more detailed images of abnormal vessels in the brain.

Treatment
Cerebral AVMs should be treated once they declare themselves and become symptomatic to avoid the drastic consequences of sudden intracranial hemorrhage from a ruptured AVM. The location and size of the AVM, as well as the patient's overall health and desire to undergo surgery must be considered in the ultimate decision as to which treatment modality is recommended.

The final goal of the treatment is to remove or cut off the blood supply to the AVM. This will prevent further growth of the AVM and eliminate the risk of rupture. Current treatment options for AVMs are surgery, embolization, radiosurgery, or a combination of these therapies.

Embolization of AVMs involves placing a long flexible catheter into a blood vessel in the groin. This catheter is then advanced through the blood vessel to reach the AVM, a glue-like material is then injected into the abnormal vessel ,thereby cutting off the blood flow to the AVM.

In many cases, surgery may be recommended to completely remove the AVM. Occasionally, embolization is used in combination with surgery to allow for an easier and less hazardous operation. Surgery for an AVM involves identifying the margins of the malformation, ligating or clipping the feeder arterial vessels, obliterating the draining veins, and removing or obliterating the nidus of the AVM.

Prognosis
Since there are a number of variables involved, it is difficult to generalize about the clinical outcome of AVMs in various settings and different treatment modalities. Approximately 10% of cases whith hemorrhage as the first symptom are fatal. Seizures and neurologic manifestations usually resolve or markedly improve with successful treatment.